Chemistry Modules 1,2,3

Revision Cards breaking down C1,C2 and C3!

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C1 - The Evolution Of The Atmosphere

  • Phase 1 - 1)Earths surface was originally molten. So hot, any atmosphere 'boiled' into space. 2)Things cooled down + a thin crust formed, but volcanoes kept erupting. 3)Volcanoes gave out carbon dioxide, water vapour + nitrogen. This is how we think the atmosphere formed. 4)The early atmosphere was mostly CO2 + water vapour with no oxygen. 5)Oceans formed when water vapour condensed when the earth cooled.
  • Phase 2 - 1)Green plants evolved over most of the earth. 2)A Lot of early CO2 dissolved into oceans. Green plants removed CO2 from air + produced oxygen by photosynthesis. 3)Plants died + were buried under layers of sediment. The carbon they had removed from the air (as CO2) became 'locked up' in sedimentary rocks as insoluble carbonates and fossil fuels.
  • Phase 3 - 1)The build up of oxygen in the atmosphere killed off some early organisms that couldn't tolerate it. However it allowed more complex organisms to evolve. 2)There is virtually no CO2 left now.
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C1 - The Atmosphere Today

Atmosphere is mostly Nitrogen (78%) Oxygen (21%) and Argon (1%). It also contains small amounts of Carbon Dioxide + various other gasses, as well as varying amounts of water vapour. The concentrations of nitrogen, oxygen +argon in the atmosphere are constant.

Human activity is adding pollutants to the air > carbon dioxide, carbon monoxide, particulates, sulfur dioxide + nitrogen oxides. Gases + particulates can be released by nature such as volcanoes, as well as humans burning fuels in power stations + vehicles.

Some pollutant gases directly harmful to humans. They can cause disease or death if you breathe in large quantities. Carbon Monoxide reduces the amount of oxygen blood can carry, leading to flu like symptoms + eventually death.

Pollutants can also harm us indirectly, by damaging the environment. Sulfur dioxide can cause acid rain, polluting rivers + lakes, which kills the fish that people catch and eat.

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C1 - Chemical Reactions - Part 1

All substances are made from tiny particles called atoms. When atoms are joined together they make molecules.

The arrangement of atoms in different substances can be shown by diagrams. This shows that air is a mixture of different gases made up of small molecules with large spaces between them. Each coloured circle represents an atom.

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C1 - Chemical Reactions - Part 2

Almost all chemical reactions involve atoms changing places. The atoms from the substances you start off with (reactants) rearrange themselves to form different chemicals (products).

(http://mail.aol.com/35834-111/aol-6/en-gb/mail/get-attachment.aspx?uid=30985970&folder=NewMail&partId=1) No atoms 'dissapear' during the reaction. If you count all the atoms in the reactants (1 carbon, 4 hydrogen + 4 oxygen), you'll see they're still in the products. This means no mass is lost during a chemical reaction. The mass of the reactants is equal to the mass of the products.

Reactants + products often have different properties. When atoms rearrange themselves in a reaction, the products have their own properties.These can be different to the properties of the reactants. E.g. carbon is a black solid and oxygen is a colourless gas. When they react together + coal burns the product is carbon dioxide (colourless gass), but with different properties from oxygen (heavier).

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C1 - Fossil Fuels - Part 1

The majority of fuels we use contain just 2 elements, carbon and hydrogen. These are known as hydrocarbons. Many hydrocarbons are fossil fuels, which are formed from the remains of dead plants and animals over millions of years. These fuels e.g. crude oil, are drilled out of the earth and refined to make useful products like petrol and diesel.

Fuels like petrol, diesel fuel + fuel oil are mixtures of hydrocarbons. At hydrocarbon is a compound of only hydrogen + carbon. The only difference between different fuels is the size of the hydrocarbons they contain. Coal is not a hydrocarbon, as it contains many impurities but it's mostly just carbon.

Burning fuels is an example of oxidation. Burning is also known as combustion and is a type of chemical reaction. When a hydrocarbon burns, the hydrogen atoms in the fuel combine with oxygen atoms from the air to make hydrogen oxide/water. Carbon atoms in the fuel combine with oxygen to make carbon dioxide. When coal burns you get carbon dioxide.

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C1 - Fossil Fuels - Part 2

Reactions where oxygen is added is called an oxidation reaction. Reactions where oxygen is lost is called a reduction reaction. Combustion is an example of an oxidation reaction. The oxygen needed to burn hydrocarbons can come from the air, or it can be in the form of pure oxygen. Hydrocarbon fuels burn more rapidly in pure oxygen than they do in the air. Pure oxygen can be obtained from the atmosphere + kept in pressurised cylinders. It can then be used, for example, in oxy-fuel welding torches. The oxygen allows the fuel to burn more rapidly so a higher temperature can be reached.

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C1 - Air Pollution, Carbon

Fossil fuels are burnt to release energy. We burn them to power vehicles + to produce electricity in power stations. The carbon based products of burning fossil fuels often pollute the atmosphere. All fossil fuels contain lots of carbon. If the fuel is burnt where there is lots of oxygen, then almost all of the carbon ends up as carbon dioxide. This adds to the carbon dioxide that's found naturally in the atmosphere. If there is not much oxygen like in a car engine, small amounts of carbon monoxide and small particles of carbon are produced too. These are all pollutants.

Carbon dioxide has the formula CO2, meaning it has 2 oxygen atoms + 1 carbon atom. It will stay polluting the atmosphere until it's removed. It can be removed naturally by plants using it up in photosynthesis. It also dissolves in rain water. Levels can still increase if human activity adds extra CO2. An increased level increases the greenhouse effect, which is warming the earth and problems such as sea level rise. Carbon monoxide only has 1 oxygen atom. It is produced if there isn't enough oxygen when fuels burn (incomplete burning). Carbon monoxide is poisonous, it can make you drowsy and sometimes kill. Particulate carbon is where tiny particles of carbon are produced in incomplete burning. If they escape into the atmosphere they float around, eventually falling to the ground as soot. Making buildings look dirty.

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C1 - Air Pollution, Sulfur

Many fuels are hydrocarbon-based, like petrol + natural gas. Some are carbon based (coal). These fuels contain impurities as they're extracted straight from the earths crust. Many impurities are harmless but some fuels contain traces of the element sulfur. When the fuel burns, so does sulfur. The sulfur atoms then combine with oxygen to produce the pollutant sulfur dioxide. So when power stations and vehicle engines burn fossil fuels, small amounts of sulfur dioxide are produced, which normally ends up in our atmosphere.

When sulfur gets into the atmosphere it stays there until it's removed. The way it normally leaves the atmosphere is in the form of acid rain. When sulfur dioxide emitted from vehicle engines + power stations reacts with moisture in clouds, dilute sulfuric acid is formed. Eventually most of this falls as acid rain, which isn't good for the environment. Acid rain causes lakes to become acidic, killing plants + animals. It also kills trees and damages buildings + statues made from some kinds of stone such as limestone.

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C1 - Air Pollution, Nitrogen

Fossil fuels burn at such high temperatures that nearby atoms in the air react with each other. Nitrogen in the air reacts with oxygen to produce small amounts of compounds known as nitrogen oxides - nitrogen monoxide + nitrogen dioxide. This happens in a car engine. Nitrogen oxides are pollutants.

Nitrogen monoxide forms when nitrogen + oxygen are exposed to a very high temperature. This happens when fuels are burnt in places like car engines. Nitrogen dioxide is produced when the nitrogen monoxide goes on to react with more oxygen in the air.

As pollutants, nitrogen oxides are very similar to sulfur dioxide. When they're formed they usually end up in the atmosphere, which is where they stay until they react with moisture in clouds. This produces a dilute nitric acid which eventually falls to the earth as acid rain. Acid rain causes lakes to become acidic, killing plants + animals. It also kills trees and damages buildings + statues made from some kinds of stone such as limestone.

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C1 - Reducing Pollution

The simplest way to reduce all types of pollution is to use less electricity, this means less fossil fuels would need to be burnt. 1)Much of the sulfur can be taken out of natural gas + fuel oil, meaning less sulfur dioxide is produced when it burns. 2)When coal's burnt in power stations, most sulfur dioxide + particulates (carbon + ash) can be removed from the flue gases before they're released into the atmosphere. It is removed by reacting with an alkali (wet scrubbing). Sulfur dioxide can be dissolved in seawater, producing CO2 + dissolved sulfate. The other alkali is an alkaline slurry. The slurry is sprayed onto gases, sulphur dioxide reacts with calcium oxide. Solid waste product (calcium sulfate) is formed. 3)The only way to reduce CO2 emissions is to reduce the amount of fossil fuels burnt, by using less electricity or finding alternative energy sources.

Cars are fitted with catalytic converters. They convert nitrogen monoxide to nitrogen + oxygen (reduction reaction). They convert carbon monoxide to carbon dioxide by adding oxygen (oxidation). There's a legal limit on the amount of emissions cars can give out. These are checked once a year in an MOT. Pollution can be reduced by using our cars less and using public transport. Or people could use bio-fuels(renewable) to run their car. Or using electric batteries.

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C2 - Natural and Synthetic Materials

Every material is made up of chemicals. Chemicals are made up of atoms or groups of atoms bonded together. Some materials are mixtures of chemicals. A mixture contains different substances that aren't chemically bonded together. For example rock salt is a mixture of 2 compounds, salt + sand.

Some materials occur naturally. These are made by other living things not humans. Materials from plants - Wood and paper are made from trees, cotton comes from the cotton plant. Materials from animals - Wool from sheep, silk is made by the silkworm lava, leather from cow.

Synthetic materials are made by humans. Rubber used to come from the sap of the rubber tree. A lot of rubber is still got this way (car tyres), but you can make it in a factory. The advantage is you can control the properties, making it suitable for certain things. Lots of clothes are made of synthetic fabrics like nylon + polyester. The properties can then be controlled, e.g can be made water-proof, super-stretchy etc. Most paints are mixtures of man-made chemicals. The pigment + stuff that holds it together are designed to be tough + stop colour fading. The raw materials used to make synthetic materials come from the earth's crust. E.g. aluminium + chromium are used in metal alloys.

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C2 - Materials and Properties

Melting point - The temperature where the solid turns into a liquid.

Strength - how good a material is at resisting a force. Strength is judged by how much force is needed to break or permanently change its shape. Tensile strength is how much a material can resist a pulling force e.g ropes/cables. Compressive strength is how much it can resist a pulling force e.g. bricks. Cross beams need both.

Stiffness - it's good at not bending when a force is applied(not the same as strength). Steel is very difficult to bend, because it is stiff. Some types of rubber are strong but they bend and stretch easily. They are not stiff.

Hardness - This is how difficult it is to cut into a material. The hardest material found is diamond. Diamond can only be cut with another diamond. Many industrial drills have diamond tips.

Density - A materials mass per unit volume (e.g. g/cm³) Don't confuse density with mass or weight. Gold is very dense, air is not. Density is the volume of the object.

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C2 - Materials, Properties and Uses

Plastics - fairly hard strong + stiff. Some are fairly low density + some are moldable. Rubber - strong but soft + flexible. It is also moldable.                                                 Nylon Fibres - soft and flexible. Good tensile strength.

A products properties depend on the material its made from, this determines the effectiveness too. Materials also effect a products durability. Gramophone records 100 years ago were made of a mixture of materials like paper, slate + wax. They broke very easily because they weren't strong. Modern records are made of polyvinyl chloride (PVC) or vinyl. This material is strong + flexible so it's less likely to break. Most people nowadays own compact discs (CD), made of polycarbonate. It's very tough + flexible. It's also used in bullet proof glass + should last longer than PVC.

You need to look at properties of a material + work out what sort of purposes it's suitable for. Cooking utensils made with something with a high melting point + non-toxic. Toy car must be non-toxic, strong, stiff + low density. Clothing fabric mustn't be stiff but needs good tensile strength + a high flame resistance especially for nightwear or children's clothes.

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C2 - Crude Oil

 Crude Oil is a mixture of hydrocarbons. These are molecules that are made of chains of carbon + hydrogen atoms only. As the length of the chain changes, the properties of the hydrocarbon change. Shorter the chain, lower the boiling point (often gases), longer the chain, higher the boiling point + can be viscous(thick/sticky).

There are 2 types of bond in crude oil, strong covelant bonds between carbons + hydrogens within each hydrocarbon molecule + intermolecular forces of attraction between different hydrocarbon molecules in the mixture.

When the crude oil mixture is heated, molecules are supplied with extra energy, making them move about more. Eventually one might have enough to overcome intermolecular forces that keep it with other molecules. It can then whiz off as a gas. The covalent bonds holding each molecule together are stronger than intermolecular forces so they don't break. The intermolecular forces break easier in small molecules because the forces are much stronger between big molecules. Big molecules have higher boiling points because more energy is needed for them to break out of a liquid and form a gas.

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C2 - Uses of Crude Oil

The process of separation Crude Oil is refining, which is done by fractional distillation. During this process, hydrocarbons are separated into groups with different boiling points. Each group is called a fraction. Hydrocarbon chains have similar boiling points if they are similar in length. The uses of hydrocarbon depend on the length of its molecule chains.      

Most Hydrocarbons in crude oil are used to produce fuels. Some of the less useful hydrocarbons can be split apart to make more useful hydrocarbons and ethene, which is really useful for making plastics. The process of making new compounds is called chemical synthesis.

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C2 - Polymerisation

Plastics are formed when lots of small molecules(monomers) join together to make a very large molecule(polymer). They're usually carbon based. Under high pressure, many small molecules polymerise to form long chains(polymers).

Different polymers have different physical properties, some stronger, some stretchier etc. Strong, rigid polymers e.g. high-density polythene are used to make plastic milk bottles. Light, stretchable ones e.g. low-density polythene are used for plastic bags. It has a low melting point. PVC can be made to be either rigid(window frames + piping) or stretchy(synthetic leather). Polystyrene foam is used in packaging to stop things breaking, also to make disposable coffee cups(trapped air in foam makes it a good thermal insulator). Heat-resistant polymers e.g. melamine resin + polypropene are used to make plastic kettles.

Polymers have replaced natural materials for some uses. Nylon and polyester often replace cotton, wool or silk. They tend to be lighter, more durable, water-resistant + often cheaper. Sometimes however, synthetic fibres are uncomfortable to the skin. Rigid PVC has replaced wood for window frames, because it is water-resistant, strong + durable, making windows more secure. The disadvantage is that they don't look as good as wooden ones.

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C2 - Structure and Properties of Polymers

If polymer chains are packed closely together, the material has high density. If the chains are spread out, the material will have low density.

The forces between chains hold it together as a solid mass. Chains held together by weak forces are free to slide(plastic can stretch + low melting point). Plastics with stronger bonds have higher melting points + can't be stretched as crosslinks hold chains firmly together. Stronger the bonds, the more energy needed to break apart.

Polymers can be chemically modified to change their properties. They can be modifies to increase the chain length. Short chained polymers are easy to shape + have lower melting points. Polymers can be made stronger by adding crosslinking agents which chemically bond the chains together making the polymer stiffer, stronger + heat resistant. Plasticisers can be added to a polymer to make it softer + easier to shape. They work by getting in between polymer chains + reducing forces between them. The polymer can be made more crystalline, these have straight chains with no branches so the chains can fit closely together. Crystalline polymers have higher density, are stronger + have higher melting points.

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C2 - Nanotechnology - Part 1

Really tine particles, 1-100 nanometres across are called nanoparticles. Nanotechnology is the branch of technology making + using nanoparticles. Some of the structures that are dealt with are only as big as some molecules, so nanotechnology involves understanding how to control matter on a very small scale.

Most nanomaterials are made using nanotechnology, but some nanoscale materials occur naturally e.g. Seaspray - the sea produces nanoscale salt particles which are present in the atmosphere. Combustion - when fuels are burnt, nanoscale soot particles are produced.

Nanoparticles can be added to materials to give them different properties. They are added to plastics in sports equipment e.g. tennis rackets, golf clubs + golf balls. They make plastic stronger + more durable + don't add weight. Silver nanoparticles are added to polymer fibres used to make surgical masks + wound dressings. It gives the fibres antibacterial properties. Nanoparticles have a larger surface area to volume ratio which gives them different properties.

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C2 - Nanotechnology - Part 2

Although they are useful, the affect on the body isn't fully understood so they have to be tested to minimise the risks. Some people worry that they products are made available before the effects have been investigated. As long-term impacts aren't known, people believe products containing nanoparticles should be labelled.

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C3 - Tectonic Plates

The earth's spherical + has layered structure. The crust + upper part of the mantle (hot flowing solid) are cracked into large pieces - tectonic plates. The plates float on the mantle. They move around, most of the plates move at speeds of a few cm per year relative to eachother. Meaning different parts of the world as we know it have been located at positions + have moved slowly over the earth's surface.

When tectonic plates move away from eachother under the sea the exposed mantle rises up through the seafloor + solidifies to form new crust. When it forms it's magnetised by the earth's magnetic field. Every half a million years the magnetic field swaps direction so the rocks have normal or reversed polarity when cooled. The pattern of normal + reversed polarised rocks is used to estimate the age of parts of the earth's crust, + track the very slow movement of the plates.

As tectonic plates move, rocks found today may have been formed in different positions on the surface of the earth, + different climates. Geologists look at features of rocks to learn about where they were formed. Fossils - remains/imprints of dead organisms. Tell you the age of the rock + conditions it was formed in. Rock formed underwater can contain shells + ripples created by sea or rivers. The sediment that forms rocks is carried by water/air. Looking at the shape of grains in sedimentary rocks you can tell if its formed in water(water-borne grains) or on the surface(air-blown grains).

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